Alloy article for use at elevated temperatures



Patented July 4, 1950 ALLOY ARTICLE FOR USE AT ELEVATED TEMPERATURES Russell Franks and William 0. Binder, Niagara Falls, N. Y., assignors, by mcsne assignments, to Union Carbide and Carbon Corporation, a

I corporation of New York No Drawing. Application May 9, 1946,

Serial No. 668,327

4 Claims. (01. 75-122) This invention relates to heat resistant alloy articles designed particularly for use in applications where great strength at very high temperatures is required The continued development of such devices as superchargers, gas turbines, jet propulsion apparatus and the like depends upon the production of workable metals and alloys that are strong at the high temperatures at which such devices operate. Although several alloys have been proposed for use in high temperature applications, the utility of such alloys has been limited either because they are not hot-workable or machinable or because they become brittle upon continued exposure to elevated temperatures. One characteristic of highly alloyed ferrous metals which complicates the problem considerably is that as the iron-base solid solution is more heavily loaded with alloying materials to increase the high-temperature strength, the high-temperature stability tends to decrease so that upon prolonged heating the material becomes unduly brittle.

There is accordingly a need for hot-workable, machinable alloy articles having great strength and stabilit at highly elevated temperatures, and it is the principal object of this invention to satisfy this need.

In our copending application Serial No. 599,306, filed June 13, 1945, and issued December 16, 1947, as Patent No. 2,432,615, we disclosed a new ironbase alloy containing nickel, chromium, cobalt, molybdenum, tungsten, and at least one metal selected from the group consisting of columbium, tantalum, titanium and vanadium, as the principal constituents, together with re atively minor though essential amounts of manganese, silicon, carbon and nitrogen. This alloy is workable, machinable, and has great strength and stability at high temperatures. We have now found that by raising the tungsten content of the former alloy its strength at high temperatures is significantly increased and, surprisingly, its hot workability is not seriously impaired. The present invention accordingly comprises a heat resistant alloy article containing chromium; nickel, cobalt, tungsten, and at least one metal from the group consisting of columbium, tantalum, titanium, and vanadium, together with minor quantities of manganese, silicon, molybdenum, carbon, nitrogen and impurities commonly present in steels of good quality.

Specifically, the alloy of the present invention contains by weight 15% to 25% chromium; 15% to 25% nickel; to 25% cobalt; more than 7.5%, preferably more than 10% but not more than tungsten, an aggregate of 0.5% to 3% of one or more of the elements columbium, tantalum, titanium, and vanadium; and up to 2% manganese, up to 1% silicon, up to 0.35% carbon, 0.05% to 0.25% nitrogen; and the remainder substantially all iron and incidental impurities. Up to about 3.5% molybdenum may be present, but additional molybdenum imparts no substantial benefit. The content of any single element of the columbium, tantalum, titanium, vanadium group should be less than 2%, and the titanium content should not exceed 1.5%. Somewhat more of the minor constituents than the upper limits just specified may on occasion be used. For instance, if excellent forgeabilityis not essential, the carbon content may be above 0.35%, up to say 1%. Iron is present in a substantial proportion, the iron content being at least 15% and preferably at least 20% of the alloy.

Alloys within the foregoing composition ranges are readily forged, welded, and machined and, as has been demonstrated by test, have remarkably great strength and stability at high temperatures, for example 1200 F. and upwards. Machine parts of the alloys may be designed to operate at high stress for long periods of time at 1500 F. and at lower stress for moderate periods at somewhat higher temperatures. The invention includes cast or hot-worked articles and welded articles for use at elevated temperatures and composed of such alloys.

A useful test for determining the suitability of metals and alloys for high temperature applications is the so-called stress-rupture test. In this test, each of several samples of a given material is subjected to a measured tensile stress at a particular elevated temperature, and the time required for the sample to fail under these conditions of temperature and stress is noted. The data obtained are then plotted, using time and stress as abscissa and ordinate respectively. A curve is thus established for the material tested, showing for the selected temperature the time required to cause failure of the material when a particular stress is applied. Usually curves are established for several different temperatures, and from these curves can be predicted quite -accurately the length of time the material can withstand failure at a given stress applied at a given temperature. This information is valuable for design purposes, especially if the material selected may be subjected to overheating, overloading, or both.

In the table results obtained on testing several alloys typical of the invention are set forth. The specimens were tested 'in both the as-forged condition (condition 1) and after having been forged, heated one hour at about 2300" F. and quenched in water (condition 2) The specimens were tested at 1500 F. and 20,000 pounds per square inch stress. Time to failure under these conditions is reported in hours.

the ranges given may be used, but it the alloy will be used where exposure to temperatures above 1350 F. is probable, compositions near the upper limits of the ranges given should be employed. If the alloy is to be used where temperatures not in excess of 1200 F. will be encoun- The data in the above table illustrate the high strength of the alloy of the invention at elevated temperatures and its ability to withstand large stresses at high temperatures for prolonged periods of time. The data also afford a comparison of the alloy of the invention with an alloy disclosed in our copending application above referred to. The first alloy in the table is one having a composition within the ranges of our copending application. The remaining alloys are the subject of the present invention. It will be seen that they withstood the test conditions for from about two times to nearly six times as long before failure as the first alloy in the table.

The alloy of the invention may be forged or otherwise hot-worked without difliculty in the range of 2100" F. to 1600 F. In some cases working should be continued to a temperature somewhat below the recrystallization temperature (about 1200 F.). An alloy so wrought is said to be in the cold hot-worked condition. The alloy is also easily machinable and has good cold or hot bending and forming properties because of its high ductility.

Another important advantage of the alloy of this invention is that it may be welded by ordinary welding methods including the various electric arc and oxyacetylene fusion-deposition methods, submerged-melt electric methods and solid-phase pressure welding methods, the welds produced being sound, tough, and ductile both in the weld zone itself and in areas adjacent to and remote from the weld zone.

To ensure the attainment of the desirable characteristics of the alloy of the invention it is most important that the composition limits set forth be adhered to so that the alloying elements are present in the proper proportions. For example, nitrogen is beneficial to high temperature properties in the range given, but too high a nitrogen content is detrimental. Similarly if the proportions of molybdenum, tungsten, columbium, tantalum, titanium, vanadium, and carbon be higher than the ranges given, the alloy suffers in hotworkability and weldability; welds made in such alloys lack toughness and ductility. The deleterious effects of too high proportions of these elements cannot satisfactorily be offset by increasing the proportions Of cobalt and nickel in the alloy. Accordingly, care should be taken that the composition limits described be observed in making the alloy.

If the alloy is intended for uses in which it will be exposed to temperatures not in excess of about 1850 F. compositions near the lower lim ts tered, it may be used in the cold hot-worked condition, but where exposure to temperatures above 1200 F. is expected, the alloy should be annealed at a temperature of about 2200 F. to 2320 F. before use for best service.

Typical of articles for which the alloy of the invention is well suited are blades, wheels and other parts of turbines. Such articles may be either cast or wrought.

Although particular emphasis has been laid on the hot working properties of the alloy of the invention and the use of the alloy for wrought articles, castings of the alloy also possess very useful properties at high temperatures.

We claim:

1. A heat resistant alloy article which in normal use is exposed to elevated temperatures upwards of 1200 F. and has great strength and stability when subjected to high stresses at such elevated temperatures, said article being composed of a machinable, weldable, castable and hot-workable alloy containing: 15%. to 25% chromium; 15% to 25% nickel; 10% to 25% cobalt; at least 10% but not more than 15% tungsten; 0.5% to 3% in the aggregate of at least one element selected from the group consisting of columbium, tantalum, titanium and vanadium, the amount of any single element of said group being less than 2% of the alloy and the titanium content not exceeding 1.5%; carbon in an eifective amount up to 1.0%; 0.05% to 0.25% nitrogen; the remainder iron and incidental impurities, the iron content being at least 15%.

2. A heat resistant alloy article which in normal use in exposed to elevated temperatures upwards of 1200 F. and has great strength and stability when subjected to high stresses at such elevated temperatures, said article being composed of a machinable, weldable, castable and hot-workable alloy consisting of 15% to 25% chromium; 15% to 25% nickel; 10% to 25% cobalt; at least 10% but not more than 15% tungsten; 0.5% to 3% in the aggregate of at least one element selected from the group consisting of columbium, tantalum, titanium and vanadium, the amount of any single element of said group being less than 2% of the alloy and the titanium content not exceeding 1.5%; manganese in an effective amount up to 2%; silicon in an effective amount up to 1%; carbon in an effective amount not greater than 0.35%; 0.05% to 0.25% nitrogen; the remainder lron and incidental impurities, the iron content being at least 20% of the alloy.

3. A, heat resistant alloy article which in normal use is exposed to elevated temperatures upwards of 1200 F. and has high strength and stability when subjected to high stresses at such elevated temperatures, said article being composed of a machinable, weldable, castable and hot-workable alloy consisting of 15% to 25% chromium; 15% to 25% nickel; to 25% .cohalt; up to 3.5% molybdenum; at least 10% but not more than tungsten; 0.5% to 3% in the aggregate of at least one element selected from the group consisting of columbium, tantalum, titanium and vanadium, the amount of titanium not exceeding 1.5% of the alloy and the amount of any other element of said group being less than 2% of the alloy; manganese in an amount up to 2%; silicon in an amount up to 1%; carbon in an amount not greater than 0.35%; 0.05% to 0.25% nitrogen; the remainder all iron and incidental impurities, the iron content being at least 15% of the alloy.

4. A hot-worked heat resistant alloy article which in normal use is exposed to elevated temperatures upwards of 1200 F. and has great strength and stability when subjected for prolonged periods of time to high stresses at such elevated temperatures, said article being composed of a hot-workable alloy consisting of 15% to chromium; 15% to 25% nickel; 10% to 25% cobalt; 0% to 3.5% molybdenum; more than 10% but not more than 15% tungsten; 0.5% to less than 2% columbium; manganese in an effective amount up to 2%; silicon in an efiective amount up to 1%; carbon in an effective amount up to- 0.35%; 0.05% to 0.25% nitrogen; the remainder iron and incidental impurities, the iron content being at least 20 of the alloy.

RUSSELL FRANKS. WILLIAM O. BINDER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,729,154 Clawson Sept. 24, 1929 1,774,862 Wissler Sept. 2, 1930 2,245,366 Rohn June 10, 1941 2,246,078 Rohn June 17, 1941 2,309,371 Wissler Jan. 26, 1943 2,398,702 Fleischmann Apr. 16, 1946 2,432,615 Franks et al. Dec. 16, 1947 2,432,618 Franks et al. Dec. 16, 1947 FOREIGN PATENTS Number Country Date 219,293 Great Britain May 7, 1925 371,334 Great Britain Apr. 13, 1932 OTHER REFERENCES Kinzel and Franks: Alloys Iron and Chromium, vol. II, 1940, pages 87, 88, 180, 192-194, 455. Published by McGraw-Hill Book Co., N. Y.

Progress Report on NDRC, Research Project, NRC-8, P. B. 39, 578, October 7, 1942, pages 1-21 inclusive (particularly page 5). Declassifled to open January 28, 1946. 

1. A HEAT RESISTANT ALLOY ARTICLE WHICH IN NORMAL USE IS EXPOSED TO ELEVATED TEMPREATURES UPWARDS OF 1200*F. AND HAS GREAT STRENGTH AND STABILITY WHEN SUBJECTED TO HIGH STRESSES AT SUCH ELEVATED TEMPERATURES, SAID ARTICLE BEING COMPOSED OF A MACHINABLE, WELDABLE, CASTABLE AND HOT-WORKABLE ALLOY CONTAINING: 15% TO 25% CHROMIUM; 15% TO 25% NICKEL; 10% TO 25% COBALT; AT LEAST 10% BUT NOT MORE THAN 15% TUNGSTEN; 0.5% TO 3% IN THE AGGREGATE OF AT LEAST ONE ELEMENT SELECTED FROM THE GROUP CONSISTING OF COLUMBIUM TANTALUM, TITANIUM AND VANADIUM, THE AMOUNT OF ANY SINGLE ELEMENT OF SAID GROUP BEING LESS THAN 2% OF THE ALLOY AND THE TITANIUM CONTENT NOT EXCEEDING 1.5%; CARBON IN AN EFFECTIVE AMOUNT UP TO 1.0%; 0.05% TO 0.25% NITROGEN; THE REMAINDER IRON AND INCIDENTAL IMPURITIES, THE IRON CONTENT BEING AT LEAST 15%. 